If a user provided callback to setcookiegeneratecallback returned a cookie value greater than 256 bytes, pyOpenSSL would overflow an OpenSSL provided buffer.

Cookie values that are too long are now rejected.

If a user provided callback to settlsextservernamecallback raised an unhandled exception, this would result in a connection being accepted. If a user was relying on this callback for any security-sensitive behavior, this could allow bypassing it.

Unhandled exceptions now result in rejecting the connection.

Credit to Leury Castillo for reporting this issue.

It was discovered that pyOpenSSL incorrectly handled memory when handling X509 objects. A remote attacker could use this issue to cause pyOpenSSL to crash, resulting in a denial of service, or possibly execute arbitrary code. This attack appears to be exploitable via Depends on the calling application and if it retains a reference to the memory. This vulnerability appears to have been fixed in 17.5.0.